Many integrated circuit designs use a variety of cells that perform specific functions. Integrated circuits can include logic, memory, controller and other functional blocks. Semiconductor integrated circuits are fabricated in a semiconductor process, often using a CMOS process. Transistors are formed in a semiconductor substrate, and usually involve a sequence of fabrication steps that result in a gate with adjacent source and drain, the source and drain being formed in a channel. A key setting for a transistor is the threshold voltage, which in turn determines the voltage at which a transistor can be switched. Low threshold voltage devices are generally used for high speed circuits, though low threshold voltage devices tend to have higher leakage power. High threshold voltage devices tend to result in slower speeds but are usually implemented when power reduction is desired. It is generally known that variation in threshold voltage from the device specification is undesirable. Threshold voltage can be set by incorporating dopants into the transistor channel, either by way of direct channel implantation adjacent the gate oxide or by way of pocket or halo implants adjacent the source and drain. Such channel doping or halo implants also have the positive effect of reducing short channel effects especially as the gate length shrinks. Threshold voltage variation can increase with scaling, however, because of random dopant fluctuations in the implanted channel area. The variation problem worsens as critical dimensions shrink because of the greater impact of dopant fluctuations as the volume of the channel becomes smaller. As a result, circuit design has become more limited over time in that circuit designers must account for greater potential variation in the devices with smaller gate dimensions, thus making it impossible to design circuits with the technical freedom needed to build new and improved semiconductor chips. While CMOS technology has improved to allow continued scaling down of critical dimension, the associated and desired scaling down of voltage has not followed.